Late_Heavy_Bombardment

# Late Heavy Bombardment  **Microsim — three.js (Wikitube framework):** *Rock inside, gas and ice outside (Solar System explorer)* <div class="wt-sim" data-src="https://wikitube-3d-microsims.netlify.app/solar/Solar_System.html?view=composition&embed=1" data-title="Rock inside, gas and ice outside (Solar System explorer)"></div> *The Solar System explorer locked on this article's state (`?view=composition`); every object and population of the [[PORTAL_Solar_System|Solar System portal]] has its own state in the same scene.*  *Try: press l to show the labels and find the Moon beside Earth, the body whose Apollo samples first suggested a late spike in impacts, then Mercury, whose old cratered plains are compared with the Moon's; drag to a view from above and trace the asteroid belt between Mars and Jupiter and the giants beyond, the two reservoirs most often proposed as the impactors' source; press o to hide the orbits and compare the planets by colour.* The **Late Heavy Bombardment** (LHB), also called the **lunar cataclysm**, is a hypothesised period, roughly 4.1 to 3.8 billion years ago, during which the [[Moon]] and the other bodies of the inner Solar System were struck by an unusually large number of [[Asteroid|asteroids]] and [[Comet|comets]].[^bottke2017] The idea rests mainly on lunar rocks returned by the Apollo missions: many impact-melt samples gave ages clustered in a narrow interval, suggesting that many of the Moon's great basins formed within a short time.[^tera1974][^crockett2019] No explanation of such a spike is agreed. The best known, part of the [[Nice_model|Nice model]], is that the giant planets migrated and scattered bodies from the [[Asteroid_belt|asteroid belt]], the [[Kuiper_belt|Kuiper belt]] or both onto orbits crossing those of the [[Terrestrial_planet|terrestrial planets]].[^bottke2017] Other researchers argue that the clustering is an artefact of sampling ejecta from one large basin, and that the record fits a longer, declining bombardment from about 4.2 to 3.5 billion years ago.[^zellner2017][^boehnke2016] Once widely accepted, the cataclysm is now debated.[^mann2018] The explorer at the top of this page shows the present Solar System in its composition view: the rocky inner planets that would have been bombarded and, beyond the [[Frost_line_(astrophysics)|frost line]], the giant planets whose migration is the leading proposed cause. ## Evidence for a cataclysm The case began with the Apollo samples. Most lunar impact-melt rocks are thought to have formed when bodies tens of kilometres across struck the Moon and excavated basins hundreds of kilometres wide. Apollo 15, 16 and 17 landed near the Imbrium, Nectaris and Serenitatis basins, so their melt rocks were taken to date those basins.[^crockett2019] In 1974 Fouad Tera, Dimitri Papanastassiou and Gerald Wasserburg noted that the ages cluster between about 3.8 and 4.1 billion years and proposed a "terminal lunar cataclysm", a sharp rise in the impact rate near 3.9 billion years ago.[^tera1974] If three major basins, and by stratigraphy many others, formed in that window, the Moon must have been struck far more often than before or after.[^crockett2019] Lunar meteorites broadened the sample. They are blasted off the Moon at random locations, many from the far side, far from the Apollo sites. Impact melts in feldspathic lunar meteorites show no ages older than about 3.9 billion years, consistent with a cataclysm, although their ages spread from 2.5 to 3.9 billion years rather than clustering.[^cohen2000][^hartmann2007] Meteorites from the [[Asteroid_belt|asteroid belt]] add another line. Howardite–eucrite–diogenite meteorites, thought to come from [[4_Vesta|Vesta]], and H chondrites record many impact-reset ages between 3.4 and 4.1 billion years. Simulations show that the volume of melt an impact produces rises 100 to 1,000 times when impact speed rises from about 5 km/s, today's average in the belt, to 10 km/s. Since kinetic energy per unit mass scales as the square of speed, doubling the speed quadruples the energy delivered (derived). Speeds above 10 km/s require highly inclined or eccentric, planet-crossing orbits, rare today but common if migrating giant planets swept [[Resonance|resonances]] through the belt; the ages may therefore record such an episode.[^marchi2013] Crater size distributions on the lunar highlands and on [[Mercury_(planet)|Mercury]] suggest that the same family of impactors struck both bodies.[^strom1979] ## Criticisms of the cataclysm hypothesis The hypothesis has two principal weaknesses. The first concerns where the Apollo melt rocks came from. They were usually assigned to the nearest basin, but Imbrium, the youngest and largest nearside multi-ring basin, threw ejecta over the whole central nearside, and modelling shows that its debris should be present at every Apollo site. If most sampled melts came from Imbrium, the age cluster near 3.9 billion years records one impact, not many.[^haskin1998] A further analysis argues that the spike in argon-40/argon-39 ages can arise from episodic early crust formation followed by partial loss of argon as the impact rate declined.[^boehnke2016] The second concerns the absence of melt rocks older than about 4.1 billion years. That absence need not mean there were few older impacts: continued bombardment over four billion years may have reset the [[Radioactive_decay|radiometric]] clocks of older melts or pulverised them into grains too small to date by standard methods.[^hartmann2003] The effect resembles a survivorship bias, in which the most recent large events overprint the record of earlier ones. Newer data point the same way. Re-analyses of lunar crater ages find a record that declines steadily rather than peaking, and a 2017 review of the lunar evidence concludes that a single sharp spike is not required.[^zellner2017][^bottke2017] Argon dating of meteorites from Vesta has also been found to be in tension with a cataclysm.[^cartwright2022] Scientists continue to study the lunar samples, and the question of whether a spike occurred remains open.[^mann2018] ## Geological consequences on Earth If the Moon was bombarded, so was [[Earth]], which is larger and pulls in more impactors. Scaling lunar cratering rates to Earth suggests that the cataclysm would have produced 22,000 or more craters wider than 20 km, about 40 basins around 1,000 km across, and several near 5,000 km.[^ryder2000][^ryder2002] None survives: plate tectonics, erosion and volcanism have erased almost all of Earth's [[Crust_(geology)|crust]] of that age. The idea bears on Earth's earliest rocks. For decades the oldest known rocks clustered near 3.8 billion years, a date long taken as the end of a molten early Earth and used to mark the boundary between the Hadean and Archean eons. Rocks of the Acasta Gneiss in northwestern Canada were later dated to 4.031 ± 0.003 billion years, and a detrital zircon grain from the Jack Hills of Western Australia to 4.404 billion years.[^bowring1999][^wilde2001] Chemistry recorded in such zircons suggests that the Hadean surface was solid and had liquid [[Water|water]], not the molten world its name implies.[^wilde2001] A bombardment near 3.9 billion years could explain why so little crust survives from before it. The same question touches the origin of life. Carbon isotope ratios in rocks from Greenland, dated to about 3.8 billion years, were once read as a trace of early life; if correct, life either arose immediately after the bombardment or survived it.[^tenenbaum2002] Later studies of those rocks found no support for the original claim.[^lepland2005][^whitehouse2009] Models of the bombardment's heating show that, although the surface would have been sterilised, the subsurface and hydrothermal systems could have sheltered heat-loving microbes throughout.[^abramov2009] Large impacts continued long afterwards: in 2014 researchers reconstructed an impact about 3.26 billion years ago, near the Barberton Greenstone Belt in South Africa, by a body estimated at 37 to 58 km across.[^agu2014] ## Possible causes ### Giant-planet migration In the [[Nice_model|Nice model]] the bombardment follows an instability among the giant planets. [[Jupiter]] and [[Saturn]] begin close together, with a massive belt of planetesimals beyond the outermost giant. Scattering planetesimals makes the planets migrate slowly until Jupiter and Saturn cross their 2:1 resonance; their eccentricities rise, [[Uranus]] and [[Neptune]] are thrown into the outer belt, and a storm of comets heads inward, while resonances sweeping through the asteroid belt push asteroids onto Earth-crossing orbits.[^taylor2006][^gomes2005] Later versions start the giants in a chain of resonances, have the chain break after hundreds of millions of years, and include a "jumping Jupiter" encounter with an ice giant.[^morbidelli2007][^levison2011][^brasser2009] That jump protects the terrestrial planets but removes fewer asteroids, making an inner extension of the belt, now almost gone, the main source of impactors.[^bottke2012] Newer work finds that such impacts would not account for the ancient spherule beds on Earth or the lunar basins, and that the asteroid belt was probably not the bombardment's source.[^johnson2016][^nesvorny2017] ### Late formation of Uranus and Neptune Early planet-formation models suggested that at their present distances, where material is sparse and orbits slow, Uranus and Neptune could have taken billions of years to grow, and their late assembly was proposed as a trigger for the bombardment.[^nakano1987][^taylor2001] Later models that include gas accretion find instead that giant planets must form within the lifetime of the gas disc, about ten million years, far too early to explain an event hundreds of millions of years later.[^lin2008] ### Planet V hypothesis The Planet V hypothesis adds a fifth terrestrial planet, less than half the mass of [[Mars]], orbiting between Mars and the asteroid belt. Perturbations from the other planets eventually destabilise its orbit, it plunges through the inner belt and scatters asteroids onto Earth-crossing orbits, and it is later lost, probably into the Sun. Simulations show that the mechanism works only if the belt's asteroids were concentrated toward its inner edge.[^brasser2011] A variant proposes that the lunar impactors were debris from Planet V striking Mars and forming its northern Borealis basin, explaining why lunar basins are few relative to craters and why cometary impactors are hard to find.[^minton2015] ### Disruption of Mars-crossing asteroid Matija Ćuk has proposed that the last few lunar basins came from the break-up of a large Mars-crossing asteroid about the size of Vesta, a survivor of a once much larger population. Most earlier impacts would have come from that population, ending about 4.1 billion years ago; a lull followed, during which the Moon's magnetic field faded; then, about 3.9 billion years ago, a collision shattered the Vesta-sized body and sent a swarm of fragments toward Earth and the Moon. Ćuk cites the weak or absent magnetisation of the youngest basins and a change in the crater size distribution as support.[^cuk2012] Both the timing and the cause of that change are disputed.[^fassett2012][^marchi2012] ### Other potential sources Several other sources have been examined and mostly ruled out. Extra satellites of [[Earth]] would have been caught in resonances as the young [[Moon]]'s orbit expanded and lost within a few million years, and lunar trojans would have been destabilised within 100 million years once the Moon reached 27 Earth radii.[^cuk2009] Leftover planetesimals from terrestrial-planet formation are depleted too fast to form the last lunar basins.[^bottke2007] Primordial co-orbitals of Earth or [[Venus]] are unlikely to have been numerous enough, given their long-term stability and the absence of survivors today.[^cuk2012horseshoe] Breaking up a single main-belt asteroid would require a parent at least 1,000 to 1,500 km across.[^ito2006] Debris from collisions among early inner planets, now lost, has also been proposed.[^volk2015] ## Exosystem with possible Late Heavy Bombardment Evidence for a similar episode has been found around Eta Corvi, a star about one billion years old. Infrared spectra from the Spitzer Space Telescope show warm dust close enough to the star for Earth-like planets to exist there, with the signatures of [[Water|water]] ice, organic material and rock that characterise [[Comet|comets]], as if icy bodies were being delivered inward in large numbers.[^jpl2011][^lisse2012] The dust's composition resembles that of the Almahata Sitta meteorite, which fell in Sudan in 2008.[^jpl2011] The system also has a colder, more massive ring of dust at about 150 AU from the star, which plays the part of a [[Kuiper_belt|Kuiper belt]] and is the likely reservoir of the incoming bodies.[^jpl2011] The star's age matters for the comparison: the proposed lunar cataclysm occurred several hundred million years after the Solar System formed, and Eta Corvi, at about a billion years, is not much older than the Sun was then. The observation shows that bombardments of the kind proposed for the early Solar System can occur around other stars; it does not establish whether one occurred here, which depends on the lunar and meteoritic evidence above.[^lisse2012][^bottke2017] ## See also - [[Nice_model]] - [[Grand_tack_hypothesis]] - [[Formation_and_evolution_of_the_Solar_System]] - [[Moon]] - [[Near-Earth_object]] ## References [^bottke2017]: Bottke, W. F.; Norman, M. D. (2017). "The Late Heavy Bombardment". *Annual Review of Earth and Planetary Sciences* 45: 619–647. https://doi.org/10.1146/annurev-earth-063016-020131 [^tera1974]: Tera, F.; Papanastassiou, D. A.; Wasserburg, G. J. (1974). "Isotopic evidence for a terminal lunar cataclysm". *Earth and Planetary Science Letters* 22: 1–21. https://doi.org/10.1016/0012-821X(74)90059-4 [^crockett2019]: Crockett, C. (16 July 2019). "How the Moon landings changed our view of the Solar System". *Knowable Magazine*. https://doi.org/10.1146/knowable-071519-1 [^zellner2017]: Zellner, N. E. B. (2017). "Cataclysm no more: new views on the timing and delivery of lunar impactors". *Origins of Life and Evolution of Biospheres* 47: 261–280. https://doi.org/10.1007/s11084-017-9536-3 [^boehnke2016]: Boehnke, P.; Harrison, T. M. (2016). "Illusory Late Heavy Bombardments". *Proceedings of the National Academy of Sciences* 113: 10802–10806. https://doi.org/10.1073/pnas.1611535113 [^mann2018]: Mann, A. (2018). "Bashing holes in the tale of Earth's troubled youth". *Nature* 553: 393–395. https://doi.org/10.1038/d41586-018-01074-6 [^cohen2000]: Cohen, B. A.; Swindle, T. D.; Kring, D. A. (2000). "Support for the lunar cataclysm hypothesis from lunar meteorite impact melt ages". *Science* 290: 1754–1756. https://doi.org/10.1126/science.290.5497.1754 [^hartmann2007]: Hartmann, W. K.; Quantin, C.; Mangold, N. (2007). "Possible long-term decline in impact rates: 2. Lunar impact-melt data regarding impact history". *Icarus* 186: 11–23. https://doi.org/10.1016/j.icarus.2006.09.009 [^marchi2013]: Marchi, S.; Bottke, W. F.; Cohen, B. A.; et al. (2013). "High-velocity collisions from the lunar cataclysm recorded in asteroidal meteorites". *Nature Geoscience* 6: 303–307. https://doi.org/10.1038/ngeo1769 [^strom1979]: Strom, R. G. (1979). "Mercury: a post-Mariner 10 assessment". *Space Science Reviews* 24: 3–70. https://doi.org/10.1007/BF00221842 [^haskin1998]: Haskin, L. A.; Korotev, R. L.; Rockow, K. M.; Jolliff, B. L. (1998). "The case for an Imbrium origin of the Apollo thorium-rich impact-melt breccias". *Meteoritics & Planetary Science* 33: 959–975. https://doi.org/10.1111/j.1945-5100.1998.tb01703.x [^hartmann2003]: Hartmann, W. K. (2003). "Megaregolith evolution and cratering cataclysm models—lunar cataclysm as a misconception (28 years later)". *Meteoritics & Planetary Science* 38: 579–593. https://doi.org/10.1111/j.1945-5100.2003.tb00028.x [^cartwright2022]: Cartwright, J.; Hodges, K. V.; Wadhwa, M. (2022). "Evidence against a Late Heavy Bombardment event on Vesta". *Earth and Planetary Science Letters* 590: 117576. https://doi.org/10.1016/j.epsl.2022.117576 [^ryder2000]: Ryder, G.; Koeberl, C.; Mojzsis, S. J. (2000). "Heavy bombardment of the Earth at ~3.85 Ga: the search for petrographic and geochemical evidence". In Canup, R. M.; Righter, K. (eds.), *Origin of the Earth and Moon*. University of Arizona Press, pp. 475–492. https://doi.org/10.2307/j.ctv1v7zdrp.30 [^ryder2002]: Ryder, G. (2002). "Mass flux in the ancient Earth–Moon system and benign implications for the origin of life on Earth". *Journal of Geophysical Research: Planets* 107 (E4): 5022. https://doi.org/10.1029/2001JE001583 [^bowring1999]: Bowring, S. A.; Williams, I. S. (1999). "Priscoan (4.00–4.03 Ga) orthogneisses from northwestern Canada". *Contributions to Mineralogy and Petrology* 134: 3–16. https://doi.org/10.1007/s004100050465 [^wilde2001]: Wilde, S. A.; Valley, J. W.; Peck, W. H.; Graham, C. M. (2001). "Evidence from detrital zircons for the existence of continental crust and oceans on the Earth 4.4 Gyr ago". *Nature* 409: 175–178. https://doi.org/10.1038/35051550 [^tenenbaum2002]: Tenenbaum, D. (14 October 2002). "When did life on Earth begin? Ask a rock". *Astrobiology Magazine*. http://www.astrobio.net/news-exclusive/when-did-life-on-earth-begin-ask-a-rock/ [^lepland2005]: Lepland, A.; van Zuilen, M. A.; Arrhenius, G.; Whitehouse, M. J.; Fedo, C. M. (2005). "Questioning the evidence for Earth's earliest life—Akilia revisited". *Geology* 33: 77–79. https://doi.org/10.1130/G20890.1 [^whitehouse2009]: Whitehouse, M. J.; Myers, J. S.; Fedo, C. M. (2009). "The Akilia controversy: field, structural and geochronological evidence questions interpretations of >3.8 Ga life in SW Greenland". *Journal of the Geological Society* 166: 335–348. https://doi.org/10.1144/0016-76492008-070 [^abramov2009]: Abramov, O.; Mojzsis, S. J. (2009). "Microbial habitability of the Hadean Earth during the late heavy bombardment". *Nature* 459: 419–422. https://doi.org/10.1038/nature08015 [^agu2014]: American Geophysical Union (9 April 2014). "Scientists reconstruct ancient impact that dwarfs dinosaur-extinction blast". http://news.agu.org/press-release/scientists-reconstruct-ancient-impact-that-dwarfs-dinosaur-extinction-blast/ [^taylor2006]: Taylor, G. J. (August 2006). "Wandering gas giants and lunar bombardment". *Planetary Science Research Discoveries*. http://www.psrd.hawaii.edu/Aug06/cataclysmDynamics.html [^gomes2005]: Gomes, R.; Levison, H. F.; Tsiganis, K.; Morbidelli, A. (2005). "Origin of the cataclysmic Late Heavy Bombardment period of the terrestrial planets". *Nature* 435: 466–469. https://doi.org/10.1038/nature03676 [^morbidelli2007]: Morbidelli, A.; Tsiganis, K.; Crida, A.; Levison, H. F.; Gomes, R. (2007). "Dynamics of the giant planets of the Solar System in the gaseous protoplanetary disk and their relationship to the current orbital architecture". *The Astronomical Journal* 134: 1790–1798. https://doi.org/10.1086/521705 [^levison2011]: Levison, H. F.; Morbidelli, A.; Tsiganis, K.; Nesvorný, D.; Gomes, R. (2011). "Late orbital instabilities in the outer planets induced by interaction with a self-gravitating planetesimal disk". *The Astronomical Journal* 142: 152. https://doi.org/10.1088/0004-6256/142/5/152 [^brasser2009]: Brasser, R.; Morbidelli, A.; Gomes, R.; Tsiganis, K.; Levison, H. F. (2009). "Constructing the secular architecture of the solar system II: the terrestrial planets". *Astronomy & Astrophysics* 507: 1053–1065. https://doi.org/10.1051/0004-6361/200912878 [^bottke2012]: Bottke, W. F.; Vokrouhlický, D.; Minton, D.; et al. (2012). "An Archaean heavy bombardment from a destabilized extension of the asteroid belt". *Nature* 485: 78–81. https://doi.org/10.1038/nature10967 [^johnson2016]: Johnson, B. C.; Collins, G. S.; Minton, D. A.; et al. (2016). "Spherule layers, crater scaling laws, and the population of ancient terrestrial impactors". *Icarus* 271: 350–359. https://doi.org/10.1016/j.icarus.2016.02.023 [^nesvorny2017]: Nesvorný, D.; Roig, F.; Bottke, W. F. (2017). "Modeling the historical flux of planetary impactors". *The Astronomical Journal* 153: 103. https://doi.org/10.3847/1538-3881/153/3/103 [^nakano1987]: Nakano, T. (1987). "Formation of planets around stars of various masses. I. Formulation and a star of one solar mass". *Monthly Notices of the Royal Astronomical Society* 224: 107–130. https://doi.org/10.1093/mnras/224.1.107 [^taylor2001]: Taylor, G. J. (21 August 2001). "Uranus, Neptune, and the mountains of the Moon". *Planetary Science Research Discoveries*. http://www.psrd.hawaii.edu/Aug01/bombardment.html [^brasser2011]: Brasser, R.; Morbidelli, A. (2011). "The terrestrial Planet V hypothesis as the mechanism for the origin of the late heavy bombardment". *Astronomy & Astrophysics* 535: A41. https://doi.org/10.1051/0004-6361/201117336 [^minton2015]: Minton, D. A.; Richardson, J. E.; Fassett, C. I. (2015). "Re-examining the main asteroid belt as the primary source of ancient lunar craters". *Icarus* 247: 172–190. https://doi.org/10.1016/j.icarus.2014.10.018 [^cuk2012]: Ćuk, M. (2012). "Chronology and sources of lunar impact bombardment". *Icarus* 218: 69–79. https://doi.org/10.1016/j.icarus.2011.11.031 [^fassett2012]: Fassett, C. I.; Head, J. W.; Kadish, S. J.; et al. (2012). "Lunar impact basins: stratigraphy, sequence and ages from superposed impact crater populations measured from Lunar Orbiter Laser Altimeter (LOLA) data". *Journal of Geophysical Research: Planets* 117: E00H06. https://doi.org/10.1029/2011JE003951 [^marchi2012]: Marchi, S.; Bottke, W. F.; Kring, D. A.; Morbidelli, A. (2012). "The onset of the lunar cataclysm as recorded in its ancient crater populations". *Earth and Planetary Science Letters* 325–326: 27–38. https://doi.org/10.1016/j.epsl.2012.01.021 [^cuk2009]: Ćuk, M.; Gladman, B. J. (2009). "The fate of primordial lunar Trojans". *Icarus* 199: 237–244. https://doi.org/10.1016/j.icarus.2008.10.022 [^bottke2007]: Bottke, W. F.; Levison, H. F.; Nesvorný, D.; Dones, L. (2007). "Can planetesimals left over from terrestrial planet formation produce the lunar Late Heavy Bombardment?". *Icarus* 190: 203–223. https://doi.org/10.1016/j.icarus.2007.02.010 [^cuk2012horseshoe]: Ćuk, M.; Hamilton, D. P.; Holman, M. J. (2012). "Long-term stability of horseshoe orbits". *Monthly Notices of the Royal Astronomical Society* 426: 3051–3056. https://doi.org/10.1111/j.1365-2966.2012.21964.x [^ito2006]: Ito, T.; Malhotra, R. (2006). "Dynamical transport of asteroid fragments from the ν6 resonance". *Advances in Space Research* 38: 817–825. https://doi.org/10.1016/j.asr.2006.06.007 [^volk2015]: Volk, K.; Gladman, B. (2015). "Consolidating and crushing exoplanets: did it happen here?". *The Astrophysical Journal Letters* 806: L26. https://doi.org/10.1088/2041-8205/806/2/L26 [^jpl2011]: NASA Jet Propulsion Laboratory (19 October 2011). "NASA's Spitzer detects comet storm in nearby solar system". Reprinted by ScienceDaily. https://www.sciencedaily.com/releases/2011/10/111019161940.htm [^lin2008]: Lin, D. N. C. (2008). "The genesis of planets". *Scientific American* 298 (5): 50–59. https://doi.org/10.1038/scientificamerican0508-50 [^lisse2012]: Lisse, C. M.; Wyatt, M. C.; Chen, C. H.; et al. (2012). "Spitzer evidence for a late-heavy bombardment and the formation of ureilites in η Corvi at ~1 Gyr". *The Astrophysical Journal* 747: 93. https://doi.org/10.1088/0004-637X/747/2/93 ## Wikipedia : Wikitube **Strict pair:** [Wikipedia](https://en.wikipedia.org/wiki/Late_Heavy_Bombardment) : [Wikitube](https://en.wikitube.io/wiki/Late_Heavy_Bombardment) · pinned revision [1374601530](https://en.wikipedia.org/w/index.php?oldid=1374601530) · 2026-09-18 ## Previous hub tags Hubs: `Life_Physics`. Portals: [[PORTAL_Solar_System]]. --- *Solar System portal child articles, wave 1 · 2026-09-18 · drafted · row SOL-037 · explorer state `?view=composition`.*